1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a transflective LCD device that selectively uses reflective and transmissive modes.
2. Discussion of the Related Art
Generally, transflective LCD devices function as both transmissive and reflective LCD devices at the same time. Since the transflective LCD devices can use both light of a backlight, and exterior natural or artificial light the transflective LCD devices are not restricted from circumstances and a power consumption of the transflective LCD devices is reduced.
FIG. 1 is a schematic perspective view of a related art transflective color liquid crystal display device.
In FIG. 1, the related art transflective LCD device 29 includes an upper substrate 15 having a transparent common electrode 13 on a black matrix 19 and a color filter layer 17, and a lower substrate 30 having a switching device “T” and gate line 34 and data line 46. The lower substrate 30 also has a pixel region “P” where a reflective plate 52 including a transmissive hole “A” and a transparent pixel electrode 64 are formed. The pixel region “P” including a reflective portion “C” is defined by the gate line 34 and the data line 46. Further, a liquid crystal layer 23 is interposed between the upper and lower substrates 15 and 30.
FIG. 2 is a schematic cross-sectional view of a related art transflective liquid crystal display device.
In FIG. 2, a related art transflective LCD device 29 includes an upper substrate 15 where a common electrode 13 is formed, a lower substrate 30 where a reflective plate 52 having a transmissive hole “A” and a transparent pixel electrode 64 over or under the reflective plate 52 are formed, a liquid crystal layer 23 interposed between the upper and lower substrates 15 and 30, and a backlight 41 under the lower substrate 30. When the related art transflective LCD device 29 is operated in a reflective mode, external natural or artificial light is used as a light source.
Operation of the related art transflective LCD device 29 for reflective and transflective modes will be illustrated considering the above-mentioned structure.
In the reflective mode, the I related art transflective LCD device 29 uses external natural or artificial light. Light “B” incident on the upper substrate 15 is reflected at the reflective plate 52 and passes through the liquid crystal layer 23. The liquid crystal molecules in the liquid crystal layer 23 are aligned by an electric field between the reflective plate 52 and the common electrode 13. Here, the transmission of the light “B” through the liquid crystal layer 23 is controlled according to the alignment of the liquid crystal layer 23 and images are displayed.
In the transmissive mode, light “F” from the backlight 41 under the lower substrate 21 is used as a light source. The light “F” emitted from the backlight 41 is incident on the liquid crystal layer 23 through the transparent pixel electrode 64. Transmission of the light “F” through the liquid crystal layer 23 is controlled according to an alignment of the liquid crystal molecules in the liquid crystal layer 23 driven by an electric field between the pixel electrode 64 under the transmissive hole “A” and the common electrode 13. Hence, images can be displayed.
FIG. 3 is a schematic plan view of an array substrate for a related art transflective liquid crystal display device.
In FIG. 3, a lower substrate 30, referred to as an array substrate, includes a thin film transistors (TFT) “T” in matrix. The TFTs act as switching devices. Each TFT “T” is connected to a gate line 34 and a data line 46. Here, a pixel region “P” is defined by the gate line 34 and the data line 46. A storage capacitor “S” is formed over a portion of the gate line 34 and connected in parallel to a transparent pixel electrode 64 of the pixel region “P”. A gate pad 36 is formed at one end of the gate line 34 and a data pad 48 is formed at one end of the data line 46. External signals are applied to the gate pad 36 and the data pad 48. The TFT “T” includes a gate electrode 32, an active layer 40 over the gate electrode 32, and source and drain electrodes 42 and 44.
FIGS. 4A to 4D are schematic cross-sectional views illustrating a fabricating process of an array substrate for a related art transflective liquid crystal display device. FIGS. 4A to 4C are taken along the line IV—IV of FIG. 3.
In FIG. 4A, after a gate electrode 32, a gate line 34 (of FIG. 3) and a gate pad 36 are formed on a substrate 30 through a first mask process, a gate insulating layer 38, i.e., a first insulating layer, is formed thereon. The gate pad 36 is disposed at one end of the gate line 34 (of FIG. 3). Next, an active layer 40b of amorphous silicon and an ohmic contact layer 40a of impurity-doped amorphous silicon are formed on the gate insulating layer 38 over the gate electrode 32 through a second mask process. The active layer 40b and the ohmic contact layer 40a of an island shape constitute a semiconductor layer 40. Source and drain electrodes 42 and 44 are formed on the ohmic contact layer 40a through a third mask process. A data line 46 connected to the source electrode 42 and a data pad 48 at one end of the data line 46 are formed at the same time. The semiconductor layer 40 is completed through patterning a portion of the ohmic contact layer 40a exposed between the source and drain electrodes 42 and 44 by using the source and drain electrodes 42 and 44 as an etching mask. Here, a capacitor electrode 50 (of FIG. 3) of an island shape also may be formed over the gate line 34 (of FIG. 3).
In FIG. 4B, a second insulating layer 50 is formed on an entire surface of the substrate 30 through depositing an insulating material. A reflective electrode 52 having a transmissive hole “A” is formed on the second insulating layer 50 through a fourth mask process of depositing and patterning a metallic material of high reflectance such as aluminum (Al).
In FIG. 4C, after a third insulating layer 54 is formed on an entire surface of the substrate 30, a drain contact hole 56, a transmissive groove 58, a gate pad contact hole 60 and a data pad contact hole 62 are formed through a fifth mask process of simultaneously patterning the first, second and third insulating layers 38, 50 and 54. The drain contact hole 56 exposes the drain electrode 44; a transmissive groove 58 corresponds to the transmissive hole “A”; a gate pad contact hole 60 exposes the gate pad 36; and a data pad contact hole 62 exposes the data pad 48.
In FIG. 4D, a pixel electrode 64 connected to the drain electrode 44 is formed on the third insulating layer 54 at the pixel region “P” through a sixth mask process of patterning a transparent conductive metallic material. A gate pad terminal 66 contacting the gate pad 36 and a data pad terminal 68 contacting the data pad 48 are formed at the same time. An align key (not shown) is simultaneously formed at a non-display region during a process of forming the gate line 34 and used to align a mask and the substrate 30.
Since the array substrate for the related art transflective LCD device is fabricated through six mask processes, the processes are complex. Accordingly, the production yield is low and the production cost is high.